The Hidden Game Behind Professional Poker

How the poker pros bet millions on their own card hands—and each other

DANIEL NEGREANU IS one of the most successful poker players in the world, the winner of six World Series of Poker championships who has racked up more than $19 million from live tournament pots. So sharp is his bluffing that he once went on a TV science show to try to fool a lie detector—and, ultimately, he succeeded.

But until recently, the 39-year-old star put some serious resources into a strategy that most fans know little about. He hedged his bets, by investing in other poker players. Two years ago, he says, he invested...